RACEMIZATION OF AMINO-ACIDS IN ALKALI-TREATED FOOD PROTEINS

Casein, lactalbumin, Promine-D (soy protein), and wheat gluten exhibit significant racemization of aspartic and glutamic acids (or their amides), phenylalanine, and alanine when subjected to 0.1 N NaOH at 65C for 3 h. In order of lability to racemization, the proteins are Promine-D casein wheat gluten lactalbumin. While racemization rates of individual amino acids vary among proteins, in any given protein, the relative rates are similar. The pHkinetics of aspartic acid racemization in casein indicate that asp is first order with respect to hydroxide concentration above pH 10. Racemization can impair nutritional values of food proteins by decreasing the amounts of the essential amino acid enantiomers present, by decreasing digestibility, and as a result of specific toxicity of certain D enantiomers. © 1979, American Chemical Society. All rights reserved.